Oxidation-reduction reactions are among the most important in the biosphere. The long term goal of this project is to obtain a better understanding of metalloenzyme redox catalysis, with an emphasis on establishing the correlations between metal site structure and catalytic function. The specific aims of the current proposal are to characterize in detail the structure, spectroscopy, and reactivity of a novel Mn containing catalase. Catalases catalyze the disproportionation of H202 to water and O2. Most catalases contain a heme active site and the properties of these catalases have been characterized in detail. Recently a new family of catalases has been discovered. These contain a binuclear Mn active site. A combination of reactivity studies, steady state kinetics, and spectroscopy will be used to characterize in detail the Mn site in the Lactobacillus plantarum Mn catalase. Spectroscopic methods to be used include UV-visible, circular dichroism and magnetic circular dichroism, magnetic resonance including EPR, ENDOR, ESEEM, and NMR, and x-ray absorption spectroscopies. Beyond their contributions to understanding Mn catalase, the proposed experiments will be important in the border context of bioinorganic chemistry. Homo-binuclear metal sites are found in a variety of proteins, including hemerythrin (Fe2 site), methane monoxygenese (Fe2 site) ribonucleotide reductase (Fe2 or Mn2 site) and Mn catalase (Mn2 site). Although these proteins perform diverse biological functions, there is evidence that some, and perhaps all, of these proteins contain oxo- carboxylato bridged dinuclear sites. Detailed characterization of the Mn catalase will help to define the structural features which are responsible for determining the reactivity properties of these different binuclear sites. In addition, characterization of Mn catalase may be helpful in understanding the properties of more complex systems, such as the photsynthetic oxygen evolving complex, which contains four manganese ions. Comparisons between Mn catalase and these other systems will help to clarify the general problem of biological redox catalysis.